I would always head space on the rim.

Normal pressures of 20K and up, will give you spring back of ~.001-.002 but, lower pressures won't blow the case back out.

For fire forming, when head spacing on the rim, set the shoulder back until it barely chambers and you won't have any trouble after that.

For QL, do the math for a tapered cylinder (head to shoulder) for both cartridges. Subtract the difference and reduce the case volume by that much. 

Frank

The saga continues. Just as I thought I have the cartridge licked I found a better solution I think. Ill find out on Monday next week when dies arrive.

So the 7.62x25 Tokarev Ive looked at before but ignored due to undersized neck (I want .325 diameter bullet and .345-6 OD neck and .349 chamber neck or there abouts/

Aha, thats the best part, its undersized. I REALLY like the 32 S&W and variants. I REALLY like 38 special brass. I REALLY like 8mm barrels and now I REALLY like 7.65 argentine barrels for donors. Basically I concluded today if one uses the tokarev FL sizer to form the 38/357/max family to 30 cal, voila, I have the rimmed variants Im after. And the body/shoulder junction at .373-4 is PERFECT for the .376 typical on a 38 special family parent case. Quasi FL size with 357 mag die and neck/shoulder with tokarev, it should happen well for .308. But that doesnt help with 8mm (intended). Had a talk with frnkeore on phone and mentioned separate reamers for this and that. Made me think.  I figured this, a 30 cal tokarev reamer, ground custom to my dimensions (a 357 max with tok shoulder and neck) will give me unlimited finish reamer for all cases, plus a BODY REAMER for a .314 and 323 variant. its a win/win. Run the 30 cal reamer in full depth. Use a neck/throat for 32 cal or a neck/throat for 8mm to make the changes needed for each caliber. Thats 9 cartridges, 3 calibers, 3 reamers, of which only one is expensive.
Thinking further, the neck sizer for TOK is only valid for forming the brass initially and also loading/sizing the 30 cal variant. I have a supply of used pistol dies and often make steel inserts  to act as neck bushing sizers. I WILL have an issue with pushing the shoulder back on the 32 and 8mm cases if true FL sizing is needed. I may have a rougher made that has an 8mm neck and make a die to just push the shoulder back. Or Ill lathe bore one to kiss the shoulder back a thou or two. Or I could use the finish reamer to make a shoulder sizer bushing.

Anyway this seems WAY more streamlined and uses fewer dies and very simple modified dies and MAYBE Ill get lucky and find the 32 ACP or H&R might neck size the 32 cal version. Ive ordered TOK dies and will make a few test cases and measure to see how far out they are. I like lee dies for the expander, making replacement expanders is simple for pistol dies for 32 and 8mm. Also Argentine barrels are avail (cheap) NOS and they will work well for 32 S&W donors.

Think I wrapped up the case forming. The 7.62 tokarev die did its job at producing a reliable 30 cal parent from 38 special (and its bigger family members). It produces a .285 long neck, .305 ID (pefect for the 30 cal variant later on), the cases stay 1.160 (minor trim for consistency), .374 shoulder and .376 case head. The longer family members will have little discernible taper as the reamer will keep the body at .376 for the balance of the length of a 357 max. Matter of fact, the TOK die kisses the shell holder and cams over to produce the EXACT dimension. Its a perfect marriage.

The original bullet is still the one IM targeting for use, the RCBS Cadet 120 grain heeled bullet, having lathe bored the base band to .328 and the forward band to .328.
It sized fully in a .325 nicely and I will order a lee push thru for .327. My bore/groove on prospective rifles will be .317/.325 typical. There may be a BIGGER one which may show itself as a poor donor, and also a .323 groove my pop up which will require bullet sizing further than .327 but everything else can stay the same. Its a .002 operating window for the chamber neck tolerances (.344-.346 actual). Body to shoulder is .765 breach face to radius. Tokarev basic shoulder, 8mm basic neck.

The 30 cal variant I have seated a monster bullet in it but for to get live measurements, since donors are all 8mm and .312-14, Ill ignore the 30 cal version.

Final rough calcs on QL produced my desired results. 1350-1450 fps, 550 fps energy at 90-100% load density using Blue Dot and 2400 speed powders. Ill end up ordering a custom die set from somewhere that will archive the print for me and not screw me for the next 13 sets I order for the same cartridge (crossing fingers)

Ill be drawing up a reamer and I may go after a rougher to cut a sizer die. Will post a question on reloading for that. 
Slugged several rollin blocks today, all are right at .325 and since I stub them, they have no fit issues, its a fresh bore at .316/17 and .3250 end to end.

Appreciate the food for though I have gotten for the last 18 months o various threads started on this topic.